Laminated glazing panel, method for making same, and method for mounting and using said glazing

ABSTRACT

The invention relates to a laminated glazing panel having at lest two sheets of glass and to a manufacturing process. According to the invention, this glazing panel has sheets of glass have undergone a strengthening treatment and at least two sheets of the glass are separated by a silicone interlayer. The invention also pertains especially to the use as a window of a vessel in which there is a high pressure and/or a high temperature and/or a high moisture content, as well as to the mounting of the said window.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laminated glazing panel, comprisingat least two sheets of glass, and to its manufacturing process.

2. Discussion of the Background

The invention will be more particularly described in the case of use asa window for a vessel for cooking under pressure, such as a pressurecooker, but it is not limited to such an application; a glazing panelaccording to the invention may also be used as a window pane or windowfor vessels where one or more of the following properties may berequired: withstanding pressure and, temperature and moistureresistance. The glazing panel according to the invention may also beused under conditions requiring none of these properties.

The glazing panel according to the invention may especially be used as awindow pane or window for an integrated or external steam generatorwhich can be used for a multitude of appliances, especially domesticappliances such as irons, steam cleaners, steam ovens, etc.

Although it is not usual to find windows on pressure cookers, it turnsout that consumer demand has led manufacturers of these devices todevise such an improvement. This improvement, or more precisely thischange, allows the consumer to monitor the food during cooking and alsoenables him to satisfy his curiosity since he can see the rapid changein the cooking of the food, this change normally being invisible sincethis type of device is impervious to light.

Such a change in these devices has already been proposed, especially inEuropean Patent Application 298,405. This document describes a lid for avessel for cooking under pressure suitable for closing or sealing off acooking appliance of the pressure-cooker type. According to thisdocument, the lid includes an opening closed off by a glazing panelcomposed of two sheets of glass bonded to each other by a bondingproduct based on a transparent polybutadiene synthetic rubber. The lidpresented in this document enables the inside of the appliance to beseen, but the extent of this remains very limited; this is because itappears that, in use, the device proposed only enables the production ofwindows having a limited diameter, allowing only very limited viewing.The approach of one's face limits the passage of light. These restricteddimensions are especially due to limited mechanical properties of theglazing panel. This document provides solutions, especially described inFIGS. 19 and 20, which get round the problem of a lack of light eitherby creating a second window, through which light penetrates, or byinstalling an electrical device which illuminates the inside of thevessel. Either of these solutions is highly advantageous, but enormouslycomplicates the production of the appliance and considerably increasesthe manufacturing costs.

Moreover, it appears that at high temperatures the glazing panel formingthe window deteriorates. The term "high temperatures" is understood tomean temperatures which are greater than the normal use temperatures butwhich may in particular be reached during misuse, for example when thereis no water present. Deterioration of the glazing panel is in fact aproblem more directly associated with the bonding layer based onpolybutadiene synthetic rubber since, when such temperatures are reachedin the cooking appliance, the bonding layer becomes brownish in colorand crazes. Its function, which is to allow one to look into theappliance, is therefore no longer fulfilled. Replacement of the windowis then necessary and therefore leads to an additional cost. Moreover,this replacement is obviously not a simple operation and requires thearticle to be returned to the factory, an operation costly in terms oftime and money; it is clear that such a window requires special andrigorous mounting in order to be able to withstand the pressures whichmay prevail in the cooking appliance.

SUMMARY OF THE INVENTION

The subject of the invention is a glazing panel having, in particular,adequate pressure-resistant, temperature-resistant andmoisture-resistance properties, especially for use as a window for apressure cooker, and overcoming the problems mentioned above, especiallyby exhibiting adequate mechanical properties in order to be produced ina size large enough for the envisaged use. Another intended use of thisglazing panel is that of a glazing panel for a steam generator enablingthe water level inside the vessel to be seen.

This subject is achieved according to the invention by a laminatedglazing panel comprising at least two sheets of glass separated by aninsert, said sheets of glass having undergone a strengthening treatment,and at least two of said sheets of glass being separated by a siliconeinterlayer.

Production of such a glazing panel enables this to be used as a viewingscreen, for example on the lid of a pressure cooker or on a wall of asteam generator, without running the risks mentioned above, especiallywith regard to temperature increases not conforming to proper use of theappliance. Furthermore, such a glazing panel also meets thepressure-withstand and moisture-resistance requirements for such anapplication.

Moreover, the glazing panel according to the invention exhibitsmechanical properties sufficient for it to be produced in a size suitedto use as a viewing screen for a pressure cooker. More precisely, andcontrary to the case mentioned above, it is possible to produce it inany shape and with a size such that it allows one's face to be close tothe window while still leaving enough room for light to enter so as tobe able to see and monitor the cooking of the food. It is alsoconceivable to produce such a glazing panel with a size, at the veryleast a surface area, comparable to that of the lid, thereby making itpossible to see the entire contents of the cooking vessel. Also withregard to the shape of the window, this may have a planar surface or anon-planar surface, and therefore may be a convex surface. In the lattercase, the window may be in the form of a cone, sphere, cylinder, etc.

According to a first embodiment of the invention, the siliconeinterlayer is based on a one-component air-curing acetic silicone.Production of the glazing panel according to this embodiment may beregarded as being satisfactory but it can lead to a relatively longproduction time and therefore to high manufacturing costs. This isbecause, during production of the glazing panel, the one-componentsilicone is deposited on one of the sheets of glass in order to becovered by the second; and during the curing phase of the silicone, thearea of exchange between the silicone and air is limited to the edge ofthe silicone layer, that is to say to that part of the silicone layervisible at the periphery of the glazing panel. Because of the smallthickness of the said interlayer, this exchange area is limited andtherefore leads to long polymerization times which increase with thearea of the glazing.

In order to avoid this concern, it is proposed in a second preferredembodiment of the invention to choose a two-component silicone. Thesilicone thus crosslinks more simply and leads to a very homogeneouslayer contrary to the first embodiment in which concentric rings mayappear, the curing rate varying with the distance from the edge of theglazing panel.

Preferably, and in order to reinforce the adhesion of the siliconeinterlayer to the glass, provision is made to deposit beforehand anadhesion primer on those faces of the sheets of glass which come intocontact with the said interlayer.

Provision is also advantageously made to keep the sheets of glass apartby the presence of spacers having a thickness of at lease 0.25 mm andpreferably of at least 0.30 mm. Such a thickness produces, on the onehand, a homogeneous interlayer and promotes, on the other hand, thecrosslinking of the two-component silicone.

With regard to the strengthening of the sheets of glass, this ispreferably carried out by thermal toughening in respect of the sheets ofglass having an outwardly oriented face and by chemical toughening inrespect of the sheets of glass of which both faces are internal; Forexample in the case of a laminated glazing panel comprising three sheetsof glass, the two external sheets are thermally toughened while thesheet in the middle is chemically toughened. The thermal tougheninginduces compressive surface stresses in the sheets of glass, thesestresses being relatively deep and allowing, even in the case ofaccidental scratching, the strengthening properties obtained bytoughening to be maintained. The chemical toughening applied to thecentral sheets also induces compressive surface stresses, but over asmaller thickness. This smaller thickness is not a drawback, it beingimpossible for the faces of such sheets of glass to be subjected to anyscratching. Moreover, should the glazing panel break, chemicaltoughening leads to the formation of relatively large sized pieces ofglass. These large pieces make it possible, in the event of an accident,to hold together, by means of the silicone interlayers, the pieces ofthermally toughened sheets of glass, said pieces being of a size lessthan those of the chemically toughened sheets of glass.

Although it is true that thermal toughening enables the mechanicalproperties of the sheets of glass to be maintained in the event ofaccidental scratching, it can in no way prevent this scratching. To dothis, the invention provides, in a more expensive embodiment, for thedeposition of a scratchproof layer on the external faces of the glazingpanel. Such a layer is, for example, a DLC (Diamond-Like Carbon) layerdeposited, for example, by CVD (Chemical Vapour Deposition), this havingthe advantage of being resistant to high temperatures.

Also preferably, the sheets of glass are shaped with a rounded profilewhich gives the sheets of glass better mechanical strength. This shapingis advantageously carried out with a fine grain and thus eliminates anyrisk of initiating defects of the flake or crack type. Elimination ofany edge defect also produces uniform mechanical strength.

The invention also provides a process for manufacturing a glazing panelconsisting of at least two sheets of glass separated from each other byspacers, in which a liquid adhesive layer is deposited on one face of atleast one sheet of glass and the spacers are deposited on the said layerso that they adhere to the sheet of glass by the end of drying of thesaid layer. According to this process, it is thus possible to fix thespacers very simply before depositing the silicone interlayer and then asecond sheet of glass.

According to a preferred embodiment of the invention, the liquidadhesive layer which has just been mentioned is a priming agent oradhesion primer which reinforces the adhesion of the silicone interlayerto the glass.

The invention also provides a method of fixing a glazing panel in thewall of a vessel, especially a vessel for cooking under pressure, suchas a pressure cooker, or a steam generator, in which the glazing panelis held in place by a peripheral seal compressed by a peripheral clamp.

According to a preferred embodiment, and more particularly in the caseof vessels in which there may be a high pressure, the glazing panel isfixed, by bearing via the said seal, to the face of the wall orientedtowards the inside of the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantageous characteristics of the invention willemerge below from the description of embodiment examples of theinvention with reference to FIGS. 1, 2 and 3 which represent:

FIG. 1, a side elevation of a glazing panel according to the invention;

FIG. 2, a plan view of a glazing panel according to the invention duringproduction;

FIG. 3, a side elevation of another glazing panel according to theinvention;

FIG. 4, a diagram of a cross-sectional view of a mounting on the wall ofa vessel;

FIG. 5, a cross-sectional side view of a vessel comprising a glazingpanel;

FIG. 6, a front view of the vessel in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a laminated glazing panel 1 according to the invention,consisting of two sheets of glass 2, 3 separated by a siliconeinterlayer 4. As mentioned previously, the shape of such a glazing panelmay be of a different type and be chosen depending on the size anddesign of the cooking appliance in question. In the case shownespecially in FIG. 2, the chosen shape is a circle whose size is suchthat it allows one's face to be close to the window while letting thelight pass through in order to be able to look into the inside of theappliance.

Before assembly, the sheets of glass 2, 3 are prepared beforehand; firstof all, the periphery is shaped so that it has a rounded profile whicheliminates any risk of initiating defects, such as a flake or crack. Theshaping thus improves the mechanical properties of the sheets of glass.The shaping is carried out with a fine grain, that is to say between 170and 200 microns. The radius of the shaped profile on the edge of thesheets depends on their thickness. It is, for example, equal to 3 mm fora thickness of 4 mm or equal to 3.5 mm for a thickness of the glasssheet equal to 5 mm. Next, the sheets of glass 2, 3 undergo a thermaltoughening treatment in order to improve their mechanical strength bycreating compressive surface stresses. Strengthening by thermaltoughening enables the mechanical properties to be maintained even inthe case of accidental scratching; this type of scratching mayespecially be caused during cleaning by the user if he employs tooabrasive an implement. This scratching remains within the realm ofaccidents since the manufacturer will warn the user, especially by meansof the operating instructions. According to the invention, if such anaccident occurs, the function of a window will be lost since the insideof the vessel will no longer be able to be seen during cooking, but thecooking nevertheless will be able to continue, the glazing panelmaintaining its properties and thus meeting the standards pertaining tothe use of a pressure cooker.

An adhesion primer is deposited on one face 5, 6 of each of the sheetsof glass 2, 3 thus prepared. The faces 5, 6 are, of course, the facesintended to come into contact with the silicone interlayer 4. Anadhesion primer is, for example, the one sold by General Electric underthe reference SS 4120. This is deposited on the glass in the form of aliquid, for example using a brush or a roller, so as to form, afterdrying, a layer having a thickness of less than one hundredth of amillimeter and more precisely about 5 microns. Drying of the adhesionprimer at ambient temperature takes about one hour. Immediately afterhaving deposited the adhesion primer and before drying it, spacers 7 aredeposited on the surface 5 of one of the two sheets of glass 3 as shownin FIG. 2. The spacers are distributed relatively uniformly on the edgesof the surface 5.

In the case shown of a circular surface 5, there are three spacers,these being placed along radii of this circle every 120°. The functionof these spacers 7 is essentially to maintain a uniform space betweenthe two sheets of glass 2, 3 and therefore, on the one hand, to keep thetwo sheets 2, 3 parallel and, on the other hand, to produce aninterlayer having an even thickness. This arrangement may especiallyprevent viewing distortions caused, for example, by refraction of thelight. The spacers 7 are advantageously placed along the border of theglazing panel in order to avoid disrupting the view through it. Inaddition, they may be completely masked by the presence of a seal goingaround the glazing panel and contributing to the fixing thereof.

The spacers may be of any shape, these possibly being balls, cubes,cylinders, etc.

In one embodiment of the invention, provision is made, for example, todeposit three spacers along the radii of the circle every 120°, thesehaving the shape of needles, for example metal needles, so that theyextend beyond the periphery of the glazing panel during assembly.According to this embodiment, after assembly the spacers or needlesexhibit a region trapped within the glazing panel, said region acting asa spacer, and a region outside the glazing panel.

After the interlayer has cured, it is possible to remove these needles,for example by pinching hold of the external region and by pulling onthis emerging end using an appropriate tool. The glazing panel thusobtained does not have any spacer, these having simply served duringpolymerization of the interlayer.

In the case of FIG. 2, the spacers are cylinders having a diameter of0.35 mm and thus guarantee a thickness of the silicone layer equal totheir diameter. Moreover, this thickness allows good crosslinking of thetwo-component silicone, which will be mentioned below.

After the adhesion primer has dried, the interlayer is formed from atwo-component silicone. This is, for example, the product sold byGeneral Electric under the reference RTV 615. To use it, the twocomponents resulting in a silicone adhesive are firstly mixed together,this being followed by a bubble-removal step so as to obtain a perfectoptical quality after assembling the laminated glazing panel accordingto the invention.

In order to produce the interlayer proper, a drop of the adhesive thusobtained is deposited, in excess, at the center of the face 5 and thenpressed using the second sheet of glass 2 which bears on the spacers. Inone embodiment, in the case of a circular glazing-panel surface, it ispossible to deposit a drop of silicone adhesive at the center of thesurface 5 of the sheet of glass 3 already covered with the adhesionprimer and with the spacers, then to spread out this drop, deposited inexcess, by centrifuging and finally to cover it with the second sheet ofglass 2. In any of the methods of forming the interlayer and theassembly, it is possible to automate the operations, especially becauseof the low viscosity of the silicone adhesive which allows precisemetering using an automatic dispenser. Curing of the silicone adhesiveis then carried out in two steps. First of all, the crosslinking isinitiated at room temperature, for approximately four hours. Then thecuring is accelerated, in an oven, so as to obtain the requiredproperties of the interlayer. This second step is, for example, carriedout at 65° C. for approximately four hours.

Moreover, the invention advantageously makes provision to deposit thecylindrical spacers 7 so that the axis of the cylinder is coincidentwith a radius of the circle. In this way, during spreading of thesilicone adhesive over the surface 5, the spacers present as small aspossible a surface of resistance to the flow of the spreading material,that is to say corresponding to the base of the cylinders. It is thuspossible to avoid any risk of disbondment of the spacers 7 duringpassage of the flow of material thereat. The choice of a cylindricalshape also contributes to good retention of the spacers during passageof the flow of material. This is because this shape and its positioningprovide a greater surface tension effect than those obtained withspacers of different shapes.

FIG. 3 shows another example of a glazing panel according to theinvention. The glazing panel 8 is composed of three sheets of glass 9,10, 11 and of two silicone interlayers holding them firmly against eachother. As in the previous case, the three sheets of glass 9, 10, 11 haveundergone edge shaping, giving the edges a rounded profile. Next, thethree sheets of glass are toughened. The sheet of glass 10, internal tothe glazing panel, is chemically toughened. This toughening improves itsmechanical properties by creating compressive surface stresses. Thistoughening therefore improves the mechanical strength of the sheet ofglass 10, and consequently that of the glazing panel 8, and moreoverleads to relatively coarse pieces should the said sheet 10 break. Thesepieces can retain, by means of the interlayers 12 and 13, the smallersized pieces of the sheets 9 and 11, the sheets of glass 9 and 11undergoing a different type of treatment in order to strengthen them; infact, the two outer sheets 9 and 11 undergo thermal toughening whichalso creates compressive surface stresses, but over a greater depth.This characteristic makes it possible in the case of scratching,especially on the external faces of the glazing panel 8, to maintain thestrengthening properties obtained. Scratches which may arise byexcessively severe cleaning do not pass beyond the depth of thecompressive surface stresses obtained by thermal toughening, andtherefore do not modify the strengthening obtained.

Next, the adhesion primer is deposited on the faces 14, 15, 16, 17 ofthe three sheets of glass. While the primer on the faces 14 and 16 ofthe sheets of glass 9, 11 is drying, the spacers are deposited. Next,assembly takes place by forming in succession the two siliconeinterlayers 12, 13, as described in the previous case. Compared to theprevious case, the glazing panel 8 thus formed exhibits mechanicalproperties, especially an increased mechanical strength, which alloweven greater window sizes to be envisaged.

Tests have been carried out, especially on a glazing panel manufacturedaccording to the embodiment shown in FIG. 1, that is to say a glazingpanel consisting of two sheets of glass separated by a siliconeinterlayer. The mechanical strength, especially the impact strength orthe pressure withstand, is satisfactory; the good tear strength of thesilicone interlayer in particular improves the mechanical properties.Tests were also carried out in order to check the temperature withstandand the moisture resistance. The results are completely satisfactoryunder the normal conditions of use of a pressure cooker. Moreover, testssimulating improper use of the pressure cooker, especially through alarge temperature rise, were also carried out.

For example, the glazing panel was heated to 250° C. for 1 in aforce-convection oven, the temperature rise taking place in 20 minutes;all the results obtained show that the glazing panel according to theinvention shows no sign of weakness and maintains its function, that isto say its transparency. The same tests were carried out on a glazingpanel as described in Document EP 298,485; crazes very rapidly appearedin the interlayer, which became brownish. The viewing screen functionwas therefore lost and, in addition, the glazing panel of Document EP298,485 became weaker, the sheets of glass possibly becomingdisconnected.

FIG. 4 illustrates a method of mounting a window 18 in a wall 19 of avessel for cooking under pressure, such as a pressure cooker. The window18 is sealed with respect to the wall 19 by the compression of a seal 20whose profile has approximately the shape of an h, the window 18 beinginserted between the legs of the h.

The tall height of the cross-section of the seal 20 is pressed againstthat face of the wall 19, oriented towards the inside of the cookingvessel, but with an orifice smaller than that of the window 18.

The window is pressed against the seal by means of a peripheral clamp 21which transfers its force onto the short leg of the h (cross-section ofthe seal).

Compression of the seal is controlled by the interposition of a spacer22 in line with each rivet 23 between the inner face of the wall 19 andthat of the clamp 21.

Having mounted the window 18, a cover 24 is provided on the externalface of the wall 19. This cover 24 thus makes it possible to conceal themounting region in the visible face of the wall 19 of the vessel. In thecase of a pressure cooker, this wall 19 is advantageously the lid.

FIG. 4 illustrates a mounting of a window in the face of a wall orientedtowards the inside of the vessel; such a mounting gives, in particular,good strength to the mounting in the case of high pressures in thecontainer.

However, the invention is not limited to such a mounting and it alsoprovides for mounting of the window in the face of a wall orientedtowards the outside of the vessel.

Such an embodiment is shown in FIGS. 5 and 6 which illustrate a vesselsuch as a steam generator.

In FIG. 5, this steam generator is shown in cross-section, from theside. The vessel 25 is especially composed of a bottom part 26 and a lid27 which has an orifice 28, for example for filling. A window 29 isfixed to a side wall of the bottom part 26.

FIG. 6 shows in greater detail the advantage of such a window 29 whichcan, for example, enable the filling level of the vessel to be seen.Also shown in this FIG. 6 is a part of the system for fixing the window29 to the wall of the bottom part 26; the presence of four fixingelements, such as rivets 30, may in fact be seen.

The glazing panel according to the invention can therefore be used as aviewing screen for a vessel for cooking under pressure, such as apressure cooker, or for another device, such as a steam generator or aninstallation which may or may not require its mechanical properties, oftemperature withstand and moisture resistance. In particular, itsmechanical properties allow the production of relatively large glazingpanels for viewing-screen applications, for example for a pressurecooker, giving a very extensive view of the contents of the vessel.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. Laminated glazing panel comprising:at least twosheets of glass separated by an interlayer, wherein the sheets of glasscomprise glass sheets which have undergone a strengthening treatment anda silicone interlayer pivotal which separate at least two of said sheetsof glass wherein the strengthening of the glass sheets is carried out bythermal toughening of first and second sheets of the glass sheets havingan outwardly oriented face and by chemical toughening with respect to athird sheet of said sheets of glass which is positioned between saidfirst and second sheets of glass.
 2. Glazing panel according to claim 1,wherein the silicone interlayer is based on a one-component aceticsilicone which polymerizes in air.
 3. Glazing panel according to claim1, wherein the silicone interlayer is a two-component silicone. 4.Glazing panel according to claim 3, wherein the interlayer adheres tothe sheets of glass via an adhesion primer.
 5. Glazing panel accordingto claim 1, wherein each said external face of the glazing panel hasscratch-proof layers.
 6. Glazing panel according to claim 1 wherein atleast one of the sheets is shaped so as to have a rounded profile. 7.Glazing panel according to one of the preceding claims, wherein thesheets of glass are spaced apart by the presence of spacers such thatthey have a thickness of at least 0.25 mm and preferably of at least0.30 mm.
 8. A glazing panel according to one of claims 1 to 4, 5 and 6wherein said sheets of glass comprise a window of a vessel having a highpressure and/or a high temperature and/or a high moisture content. 9.Process for manufacturing a glazing panel having at least two sheets ofglass separated from each other by spacers, which comprises depositing alayer of liquid adhesive on at least one face of one of said at leasttwo sheets of glass,depositing the spacers on said layer; fixing saidspacers by drying said layer; and strengthening said sheets by thermallytoughening first and second sheets of said at least two sheets of glassand chemically toughening a third sheet of said sheets of glasspositioned between said first and second sheets of glass.
 10. Processaccording to claim 9, when the glazing panel comprises at least twosheets of glass bonded to each other by the combination of a primingagent and a silicone interlayer, wherein the silicone interlayer isdeposited after being separated by the spacers.
 11. Method of fixing aglazing panel in the wall of a vessel, which comprises:depositing alayer of liquid adhesive on at least one face of a sheet of glass;depositing the spacers on said layer; fixing said spacers by drying saidlayer; strengthening said sheets by thermally toughening first andsecond sheets of said sheets of glass; chemically toughening a thirdsheet of glass positioned between said first and second sheets of glass;and holding the glazing panel in place by a peripheral seal compressedby a peripheral clamp.
 12. Method according to claim 11, which comprisesfixing the glazing panel by bearing; via the said seal, the glazingpanel against a face of a wall oriented towards an inside portion of thevessel.
 13. A vessel for cooking under pressure, a pressure cooker,having a glazing panel which formed by the method claimed in either ofclaims 11 and
 12. 14. Steam generator having a glazing panel which whichis formed according to the method claimed in either of claims 11 and 12.